Day of the Giants, by Lester del Rey - Stranger than SF

Science Fiction Book Review ★★★☆☆ Leif Svensen is kidnapped by Loki and taken to Asgard where he's put to work designing weapons for the Aesir to use against the giants when Ragnarok comes. With the help of clever dwarfs, Leif produces gunpowder grenades, explosive-tipped arrows, and fission bombs. Oh yeah, the dwarfs can refine U-235, don'tcha know? It's books like these that reveal my…